For surveying a target point, numerous geodetic surveying devices have been known since ancient times. In this case, direction or angle and usually also distance from a measuring device to the target point to be surveyed are recorded and, in particular, the absolute position of the measuring device together with reference points possibly present are detected as spatial standard data.
Generally known examples of such geodetic surveying devices include theodolite, tachymeter and total station, which is also designated as electronic tachymeter or computer tachymeter. One geodetic measuring device from the prior art is described in the publication document EP 1 686 350, for example. Such devices have electrical-sensor-based angle and, if appropriate, distance measuring functions that permit direction and distance to be determined with respect to a selected target. In this case, the angle and distance variables are determined in the internal reference system of the device and, if appropriate, also have to be combined with an external reference system for absolute position determination.
In many geodetic applications, points are surveyed by specifically configured target objects being positioned there or mounted on a movable vehicle. Said target objects consist for example of a plumb staff with a reflector (e.g. an all-round prism) for defining the measurement path or the measurement point. However, surveying systems which operate without reflectors are also possible, such as are described for example in the European patent application bearing the application number EP 10168771.3.
Modern total stations have microprocessors for digital further processing and storage of detected measurement data. The devices generally have a compact and integrated design, wherein coaxial distance measuring elements and also computing, control and storage units are usually present in a device. Depending on the expansion stage of the total station, motorization of the targeting or sighting device and—in the case of the use of retroreflectors (for instance an all-round prism) as target objects—means for automatic target seeking and tracking can additionally be integrated. As a human-machine interface, the total station can have an electronic display control unit—generally a microprocessor computing unit with electronic data storage means—with display and input means, e.g. a keyboard. The measurement data detected in an electrical-sensor-based manner are fed to the display control unit, such that the position of the target point can be determined, optically displayed and stored by the display control unit. Total stations known from the prior art can furthermore have a radio data interface for setting up a radio link to external peripheral components such as e.g. a handheld data acquisition device, which can be designed, in particular, as a data logger or field computer.
For sighting or targeting the target point to be surveyed, geodetic surveying devices of the generic type have a telescopic sight, such as e.g. an optical telescope, as sighting device. The telescopic sight is generally rotatable about a vertical axis and about a horizontal tilting axis relative to a base of the measuring device, such that the telescopic sight can be aligned with the point to be surveyed by pivoting and tilting. Modern devices can have, in addition to the optical viewing channel, a camera for detecting an image, said camera being integrated into the telescopic sight and being aligned for example coaxially or in a parallel fashion, wherein the detected image can be represented, in particular, as a live image on the display of the display control unit and/or on a display of the peripheral device—such as e.g. the data logger—used for remote control. In this case, the optical system of the sighting device can have a manual focus—for example an adjusting screw for altering the position of a focusing optical system—or an autofocus, wherein the focus position is altered e.g. by servomotors. By way of example, such a sighting device of a geodetic surveying device is described in European patent application No. 09152540.2. Automatic focusing devices for telescopic sights of geodetic devices are known e.g. from DE 197 107 22, DE 199 267 06 or DE 199 495 80.
By way of example, the construction of generic telescopic sights of geodetic devices is disclosed in the publication documents EP 1 081 459 or EP 1 662 278.
Some surveying devices with a high level of expansion in the meantime have an automatic target tracking function for prisms serving as target reflector (ATR: “Automatic Target Recognition”). For this, a further separate ATR light source and an ATR detector (e.g. CCD area sensor) sensitive to the emission wavelength of said light source are conventionally additionally integrated in the telescope.
In the context of the ATR fine targeting and ATR target tracking function, in this case the ATR measurement beam is emitted in the direction of the optical target axis of the sighting device and is retroreflected for example at an all-round prism (as target reflector) and the reflected beam is detected by the ATR sensor. Depending on the deviation of the alignment of the optical target axis from the all-round prism, in this case the impingement position of the reflected radiation on the ATR sensor also deviates from a central sensor area position (i.e. the reflection spot of the ATR measurement beam retroreflected at the prism on the ATR area sensor does not lie in the center of the ATR area sensor and therefore does not impinge on a desired position defined e.g. on the basis of calibration as that position which corresponds to the optical target axis).
If this is the case, then the alignment of the sighting device is usually slightly readjusted in a motorized manner in such a way that the ATR measurement beam retroreflected at the prism impinges highly precisely in the center of the sensor area on the ATR area sensor (i.e. the horizontal and vertical angles of the sighting device are thus iteratively changed and adapted until the center of the reflection spot coincides with the desired position on the ATR area sensor).
In order to ensure the functioning of the automatic targeting on the basis of evaluation of the position of the reflection spot of the ATR measurement beam retroreflected at the prism on the ATR area sensor, it is necessary, before the function starts, to align the sighting device with the target reflector at least approximately in such a way that the ATR measurement beam also impinges on the prism and, having been reflected from there, on the ATR area sensor. For this purpose, it is possible e.g. beforehand to effect manual targeting of the target reflector on the basis of measurement by eye or to perform an automatic coarse targeting function.
Besides the ATR fine targeting function, an automatic target tracking functionality can also be provided in a similar manner and using the same ATR components (such as ATR light source and ATR detector). After ATR fine targeting has been effected (i.e. once the sighting device is aligned with the target in such a way that the center of the ATR measurement radiation reflection spot coincides with the desired position—corresponding to the target axis—on the ATR area sensor), the sighting device can furthermore be tracked to movements of the target “live” and appropriately rapidly in such a way that the center of the ATR measurement radiation reflection spot furthermore remains as accurately as possible and always on the desired position on the ATR area sensor. It is then often stated that the target is “locked on”. Problems can occur here if the target moves so jerkily and rapidly that it disappears from the field of view of the ATR detector (i.e. ATR measurement radiation reflected at the target no longer impinges on the ATR area sensor). Other causes of an interruption of the optical link between main or total station and target object may be, for example, unfavorable environmental conditions (precipitation, fog, dust, etc.) or simply obstacles that block the optical link.
The recent prior art discloses various solution proposals for eliminating this problem.
In this case, hereinafter the designation “optical methods” relates to technologies based on light emission and/or detection in the UV to IR range, as can be generated by known laser light sources, for example. “Non-optical methods” designates technologies which either are not based on the detection of electromagnetic radiation or relate to electromagnetic radiation, for example in the case of GPS (“Global Positioning System”), in other frequency ranges.
By way of example, EP 2 141 450 describes a surveying device having a function for automatic targeting of a retroreflective target and having an automatic target tracking functionality. In order in this case, even in the event of rapid and jerky movements, to keep the target in the “locked on” state and not to lose it from the field of view of the fine targeting detector, it is proposed to record images of the target in parallel by means of an overview camera (which is sensitive in the visible wavelength range), to define a specific image excerpt as target and, with the aid of image processing, to track movements of the target (or movements of objects which move concomitantly together with the target), and thereby to make it easier for the retroreflector to be found again and locked on again in the case of the target being lost from the “locked on” state.
However, this solution proposal requires, for its implementation, highly complex image processing software and inevitably leads to a significant interruption time during target tracking by the targeting or sighting unit.
A different solution path based on a GPS (“Global Positioning System”) is proposed in U.S. Pat. No. 6,035,254. According to this patent specification, the target object is equipped with a receiver for receiving GPS data. Position information for estimating the position of the target object from received GPS data is communicated to a total station, from which the total station determines how the total station has to be aligned for sighting and tracking the target object. This technical solution appears predominantly to be intended for a first alignment step for sighting the target object. Continuous coordination of GPS data with the position determining data of the total station is not disclosed, and so it is also not possible to infer any indication of stabilizing an optical target tracking or position determining functionality by combination with a different, non-optical target tracking or movement determining functionality. In particular, there is no indication of how optical and non-optical surveying data could be mathematically continuously combined or coordinated with one another using an algorithm, and that stabilized tracking of the position of the target object could be carried out continuously with the aid of the data—coordinated with one another—of the optical position determining functionality and the non-optical movement determining functionality.
US 2009/0171618 discloses a geodetic surveying system comprising a total station with targeting unit and an optical target tracking functionality in an embodiment similar to that known from the prior art, as described above. For a solution to the problem that the optical target tracking, for example on account of rapid and/or jerky movements of the target object, is interrupted by the target object disappearing from the field of view of the targeting unit, US 2009/0171618 discloses a position determining functionality for determining a direction of movement and a movement path of a target object, that is to say corresponding to a movement determining functionality. As a technical implementation for fulfilling the movement determining functionality, an acceleration sensor mounted on the target object or in a construction vehicle at the location of the target object is described, the measured acceleration signals of which acceleration sensor are integrated by means of a supervisory unit, from which the speed of the movement and the distance covered starting from a predefined time, namely respectively the last reception of optical position determining data from the total station, are determined and stored. From the measured acceleration signals, a respective prediction is made for the position of the target object by the time of the next arrival by the optical position determining unit of the total station. The data stored previously are then overwritten. In other words, the data of the movement determining functionality are not continuously combined with the data of the optical target tracking or position determining functionality by means of an algorithm, but rather are in each case discarded until the time of the last communication of optical position determining data. Therefore, the solution to the problem as disclosed in US 2009/0171618 merely fulfils an auxiliary functionality for finding the target object again after the optical contact has been lost. However, a proposal for continuously stabilizing the target tracking process by continuously combining the data from the optical position determining functionality and non-optical movement determining functionality is not indicated, nor can it be inferred.
DE 197 50 207 discloses a geodetic surveying system comprising an inertial measurement device for fulfilling a movement determining functionality supported target tracking functionality. The inertial measurement device can comprise accelerometers and/or gyroscopes, for example. DE 197 50 207 describes various embodiments according to which the inertial measurement device can be arranged on the target object or on a targeting or sighting device and in this case measures movements of the target object or of the targeting or sighting device. As targeting or sighting device, mention is made of, for example, a measuring telescope of a theodolite or a tachymeter for fulfilling an optical position determining functionality. However a proposal for continuously stabilizing the target tracking process by continuously combining the data from the optical position determining functionality and non-optical movement determining functionality is also not indicated in DE 197 50 207, nor can it be inferred from that published patent application.